Rotary encoders are used to measure rotational characteristic of rotating parts such as motor shafts, rollers, and wheels. Known encoders comprise a passive part comprising recognizable features, such as shapes or patterns, and an active part that is able to sense those features. One of the passive and active parts may be stationary while the other moves with the rotating part such that the encoder may determine, from relative movement of the features of the passive part with respect to the active part, a rotational characteristic of the part. For example, an encoder may determine a degree of rotation or a speed of rotation of a rotating part.
Good alignment between the active and passive parts of the encoder and between the parts of the encoder and the rotating part allow the encoder to accurately determine the rotational characteristic of a rotating part.